A symmetrical z-axis gyroscope with a high aspect ratio using simple and new process

This paper reports on a symmetrical z-axis gyroscope, whose stiffness of sensing and driving mode is identical in spite of the fabrication and design errors. There is no need of the electrical tuning of frequencies for a high sensitivity because the effective masses of the driving and sensing directions are hardly changed. Furthermore, it is very simple to fabricate the gyroscope with a total chip size of 3x3.5x1mm(2) using only one mask. The gyroscope structure is fabricated on an anodic bonded 40um-thick silicon on glass. After the top silicon is etched using a deep RIE, a part of the glass under the silicon structure is etched by HF for releasing the top silicon structure. Since the depth of the etched glass under the silicon structure is about 20-30 mu m, the damping and the stiction between the structure and the glass substrate are minimized. The minimum gap and the aspect ratio of this structure is 2 mu m and 20, respectively. Without an additional frequency tuning method, it is demonstrated that the difference between the two frequencies is about 85Hz, and the noise equivalent rate is 0.01 deg/sec at 50 mTorr pressure.